The present invention generally relates to nondestructive inspection methods and systems. More particularly, this invention relates to a method and system that enables automated scanning with an eddy current probe, such as for the purpose of inspecting rotating components of turbomachines.
Various nondestructive examination (NDE) techniques have been used to perform nondestructive testing on articles. An example is eddy current probe inspection of turbine components, as disclosed in commonly-assigned U.S. Pat. Nos. 4,706,020, 6,426,622, 6,545,467 and 6,952,094, whose disclosures pertaining to the construction, operation, and use of eddy current probes are incorporated herein by reference. Components of particular interest include rotating components of gas turbines, such as the high pressure turbine (HPT) disks of gas turbine engines. In the hostile operating environment of a gas turbine engine, the structural integrity of a turbine disk within its turbine section is of great importance in view of the high mechanical stresses that the disk must be able to continuously withstand at high temperatures and rotational speeds. The blades of a turbine disk are secured in slots, typically in the form of what are known as dovetail slots, which tend to eventually form cracks over time and must therefore be monitored when opportunities arise. The ability to detect cracks with lengths of as little as 60 mils (about 1.5 mm) and even less is desirable in order to provide sufficiently early detection to avoid catastrophic failure of a turbine disk.
Since turbine disks are inspected on a regular schedule, inspection techniques that minimize downtime are preferred to reduce operating costs. Common methods of inspecting turbine disks involve handheld or semi-automated systems, which typically have inherent problems, shortcomings or disadvantages. Handheld inspection methods are prone to user-related issues that can affect the quality of the signal. As an example, an eddy current probe may tilt relative to the surface being scanned when the probe is scanned to an edge or corner of a slot, resulting in erroneous readings. Though semi-automated inspection equipment are generally capable of overcoming user-related issues of handheld methods, existing equipment are often expensive and slow due to the custom tooling needed for each part to be inspected. As such, a fully-automated method and system would be preferred in order to reduce downtime and improve the reliability of the turbine disk inspections.